The mechanism of development of prolonged post-tetanic enhancement of muscarinic cholinergic ganglionic transmission by repetitive stimulation of preganglionic nerve will be investigated in vitro with the rat superior cervical ganglion. The investigations will use extracellular recording of the atropine-sensitive spontaneous post-ganglionic afterdischarge and intracellular recording of membrane resistance, spike threshold, and bethanechol sensitivity to monitor post-tetanic enhancement of the response of muscarinic receptors. Four possible mechanisms for development of post-tetanic enhancement will be investigated. These are: (1) an alteration of membrane or cell process by activation of adenyl-and/or guanylcyclase activity, (2) an increase in the number of active muscarinic receptors, (3) an alteration in membrane properties, particularly the threshold for spike generation, of the ganglionic neuron, or (4) a long-term alteration in acetylcholine metabolism in preganglionic nerve terminals. The experiments will be done under a variety of procedures which are known to cause post-tetanic enhancement and the results will be correlated in terms of magnitude and duration of post-tetanic response with simultaneously performed electrophysiological or biochemical analyses.